Various processes are known for depositing, on a running substrate, such as a steel strip, metallic coatings consisting of a layer of metal, or several successive layers of different metals, or else metal alloys. Among these processes, mention may be made of hot-dip galvanizing and electrodeposition, or indeed the various vacuum deposition (magnetron sputtering, Joule evaporation, electron bombardment and SIP (self-induced plasma)) processes.
Vacuum deposition processes have the advantage of being environmentally friendly and of enabling virtually all known elements, but also alloys, to be deposited. When it is desired for a metallic layer to be continuously deposited on a running substrate, the problem of how to feed the deposition chamber with the metal to be deposited then arises.
A first type of coating plant is known in which the metal to be deposited is kept in liquid form by being melted in a furnace before being conveyed to the deposition zone, for example by means of a pump or else by the barometer principle. However, this type of plant is not suitable for depositing metallic elements that sublime, i.e. those which pass directly from the solid phase to the vapour phase.
A second type of coating plant is known in which the metal to be deposited is in solid form, such as for example in the form of wires, which are introduced in a regular manner therein, or else in the form of granules, which are placed inside an inert graphite crucible. These plants are able to deposit metallic elements that sublime, but the deposition process is unstable, resulting in non-uniform coating thicknesses over the course of time, and is limited in terms of heating power, preventing sufficiently high deposition rates from being achieved.